The present invention generally relates to semiconductor packaging processes, and more particularly, to a new process for making a Chip-On-Lead (COL) type package.
U.S. patent publication no. 2008/290487 discloses a lead frame for a semiconductor device and a method of packaging a semiconductor device. The lead frame has at least one row of contact terminals, a die pad for receiving an integrated circuit (IC) die, a wire for connecting the contact terminals and a bonding pad of the IC die, and a polymer isolation material. The IC die is attached to a top surface of the die pad, and then bonding pads of the IC die are electrically connected to respective ones of the contact terminals. Then the die, electrical connections, and at least a top surface of the contact terminals are encapsulated with a mold compound.
In a Chip-On-Lead (COL) package, a die is mounted directly to the pins or lead fingers of a lead frame with non-conductive epoxy. Wire bonding is then performed to electrically connect the die and lead fingers, and then molding is performed to forma standard package configuration, as shown in FIG. 1, for example.
The COL package technology has the following advantages: larger die size into the existing package; no wafer pumping required; comparable thermal performance; and qualified production.
A conventional method for assembling a COL package is shown in FIG. 2. Beginning at step 207, an epoxy screen printing is performed on a Silicon wafer. Then, at step 209, a B-stage epoxy cure is performed. At step 211, the wafer is mounted on a jig and sawn into individual dies. After the incoming of the lead frame, at step 201, the frame leads are taped. With respect to the wafer that has been mounted and sawn and the lead frame that has been taped, at step 213, a hot die attach is performed. During the hot die attach process, a silver slurry is cured at the B-stage epoxy curing step. The silver slurry then must be re-melted at the hot die attach step 213, and a hot die attach at a predetermined temperature is performed. At step 215, an epoxy oven cure is performed. Then, at step 219, wire bonding is performed. After the wire bonding, at step 221, a molding operation is performed. After molding, a marking process is performed at step 223, followed by detaping at step 205. Detaping is followed by some standard remaining backend (B/E) processes, at step 225.
In the existing COL packaging process, as mentioned above, the silver slurry is cured during the B-stage epoxy process, so this process must be extended in order to properly heat the silver slurry. Thus, one drawback with the current COL packaging process is that the process has comparatively low units per hour (UPH) versus assembly of other package types.
Also in the conventional COL packaging process, the mold compound process is completed after the completion of the epoxy cure. That is to say, turning back to FIG. 1, after completion of the epoxy cure at step 209, since the mold compound at the reverse T-shape location may not have finished, the epoxy hangs in the air in the region of the reverse T-shape. Accordingly, a potential delamination risk exists between the epoxy and the die.
In addition, an organic pollutant may be created between the surface of the die and the surface of the lead frame. If the pollutant is cleaned or removed, the bonding process will be greatly improved. However, in the existing process, since the taping is performed, if the cleaning is performed, the layer on the surface of the taping will also undergo a reaction, which, disadvantageously, introduces a new pollution source.
Accordingly, the present invention provides a new COL packaging process that does not have the above-mentioned disadvantage.